1. Field of the Invention
The present invention relates to a refractometric densitometer which measures a low concentration of a solute contained in a solvent depending upon a difference between a refractive index of the solvent and that of the solution containing the solute. More particularly, it relates to a refractometric densitometer which measures the difference between the refractive index of the solvent and that of the solution containing the solute depending upon an optical principle concerning the Fresnel reflection of vibration of a reflected light quantity when the angle of incident light on the boundary surface between the solvent and the solution containing the solute is smaller than a critical angle.
2. Description of the Prior Art
In general, it is known to use a Brice type densitometer for measuring the declination of light based on the difference of the refractive index and a Fresnel reflection densitometer for detecting the variation of energy of the reflected light as a difference of the refractive index.
The former has a square shaped cell which is prepared by bonding plural glass plate with the result that it is difficult to prepare the cell with a small volume. Accordingly, the solute separated by chromatography is diffused in a cell having a relatively large volume with the result that the effectiveness of the chromatographic separation is less than desirable. Moreover, the cell is rather expensive and the transferred solution causes a turbulent flow in the cell with the result that the variation of the optical distance and the declination of the reflected light is detrimentally affected by the turbulent flow. Therefore, it has been difficult to provide a stable apparatus of high sensitivity.
Although the latter Fresnel type densitometer is in commercial use, with this apparatus, it is necessary to adjust the optical axis of the incident and reflected light because the refractive indices of the media for measurement are different. When a rectangular prism is used for the incident and the reflected light medium, a phenomenon of refraction of the incident light on the surface of the prism causes an incident point at the bottom of the prism to be shifted. Accordingly, it is difficult to effectively measure a wide range of refractive indices.
An apparatus using a cylindrical prism for the incident and the reflected light medium has been proposed to remedy this deficiency. However, this apparatus has the disadvantage that the reflected light is focused because of the lens effect causing an error when the reflected light quantity is measured by a light detector. Further the range of angles of incident and reflected light becomes wide with the result that the optical axial adjustment is difficult to attain yielding low reproducibility. With improved chromatographic separating technology, although the degree of separation can be increased and certain samples such as biochemical materials can be obtained in very small amounts, it is quite difficult to prepare a high concentration sample.